Method and composition for inhibiting growth of microorganisms including peracetic acid and a non-oxidizing biocide

ABSTRACT

The present invention provides a composition and method of administering same for inhibiting the growth of microorganisms. The composition of the present invention includes sufficient amounts of a peracetic acid and a non-oxidizing biocide. The method of the present invention includes the step of adding sufficient amounts of the peracetic acid and the non-oxidizing biocide to industrial process waters.

BACKGROUND OF THE INVENTION

1. Reference to Related Patent

The present application is a continuation-in-part of application Ser.No.08/350,570, filed Dec. 7, 1994, by Judy G. LaZonby, entitled "Methodand Composition For Inhibiting Growth of Microorganisms IncludingPeracetic Acid and a Non-Oxidizing Biocide", now U.S. Pat. No.5,494,588, which is in turn a continuation-in-part of application Ser.No. 08/102,286, filed Aug. 5, 1993, by Judy G. LaZonby, entitled "Methodand Composition for Inhibiting Growth of Microorganisms IncludingPeracetic Acid and a Non-Oxidizing Biocide", now abandoned, thedisclosures of which are incorporated herein by reference.

2. Field of the Invention

The present invention relates generally to controlling the growth ofmicroorganisms. More specifically, the present invention relates toinhibiting the growth of microorganisms in industrial waters.

3. Background of the Invention

The presence of microorganisms in waters, especially industrial waters,is a never-ending concern for industrial manufacturers. Examples ofindustrial waters where microorganisms can interfere with industrialprocesses include: cooling tower waters; mining process waters; foodprocessing waters; sugar reprocessing waters; and the like.

In the paper industry, the growth of microorganisms in pulp and papermill waters can adversely affect finished paper products. Microbial lifedepends on nutrients, pH and temperature of a particular system. Thewarm temperatures and rich carbohydrate containing fluids of papermachines and process streams provide ideal growth conditions for avariety of microorganisms. These contaminating microorganisms arecapable of causing spoilage of pulp, furnish, or chemical additives. Themicroorganisms cause deposits that break loose and fall into the paperfurnish, resulting in quality loss and/or end product defects such asholes and spots. The end result is unstable paper or paper sold at alower value. Robertson, The use of phase-contrast microscopy to assessand differentiate the microbial population of a paper mill, TAPPIJournal, pp. 83 (March 1993).

The presence of microorganisms within industrial water systems resultsin the formation of deposits of biological origin on industrialmachines. These deposits give rise to: corrosion; breaks; increased downtime; loss of yield; high chemical costs; odors; and expensive depositcontrol programs. In the paper mill industry, slime deposit arereportedly responsible for nearly 70% of all breaks, blockages and pumpfailures. Safade, Tackling the Slime Problem in a Paper Mill, PTI, p.280 (September 1988).

Slime may be defined as an "accretion or accumulation caused by certainmicroorganisms in the presence of pulp fiber, filler, dirt and othermaterials, mixed in varied proportions, having variable physicalcharacteristics and accumulating at continuously changing rates." Id. Inmost industrial process waters, especially pulp and paper mill systems,spore forming bacteria and Pseudomonas aruginosa contribute to slimeformation. The later is most prevalent in paper mill slimes. Fungi isalso a contributor of slime formation.

The conventional method of controlling microbial growth is through theuse of biocides. Biocides are generally divided into two main groups:oxidizing; and non-oxidizing. These biocides act on the microorganismsin one of three ways: either by attacking the cell wall; the cytoplasmicmembrane; or the cellular constituents. Id. at 282.

While biocides do inhibit microbial growth, economic and environmentalconcerns require improved methods. A problem with the use of biocides isthat high levels of expensive chemicals are needed to control microbialgrowth. To date, none of the commercially available biocides haveexhibited a prolonged biocidal effect. Their effectiveness is rapidlyreduced as a result of exposure to physical conditions such astemperature or association with ingredients contained by the systemtoward which they exhibit an affinity. This results in a restriction orelimination of their biocidal effectiveness.

Therefore, the use of such biocides involves continuous or frequentadditions to paper mill systems. Further, these additions must be madeat a plurality of points or zones in the system. The costs of thebiocides and the labor costs involved are considerable.

Moreover, such chemicals are highly toxic in the quantities known to berequired for effective control of microbial populations. As a result,environmental regulations restrict the amount of biocides that cansafely be discarded into the environment.

Therefore, a need exists for improved methods for controlling the growthof microorganisms in industrial process waters.

SUMMARY OF THE INVENTION

Pursuant to the present invention, the growth of microorganisms can beinhibited without the use of high levels of certain biocides. Thepresent invention provides compositions to be used for controlling thegrowth of microorganisms in industrial process waters. The compositionsinclude sufficient amounts of a peracetic acid and a non-oxidizingbiocide. The composition of the present invention possesses unexpectedsynergistic activity against microorganisms, including bacteria andfungi. Peracetic acid is an organic biocide previously only used in theU.S. in the food industry at high concentrations. (0.1-1% product).

The present invention also provides a method for inhibiting the growthof the microorganisms in industrial process waters. Preferably, theseprocess waters may be selected from the group consisting of pulp andpaper mill process waters, industrial cooling waters and mining waters.The method includes the step of adding to the waters sufficient amountsof a peracetic acid (PAA) and a non-oxidizing biocide. Combining theperacetic acid with the non-oxidizing biocide has been found to enhancethe effectiveness of the non-oxidizing biocide.

In an embodiment, the biocide is chosen from the group consisting of:isothiazolin; glutaraldehyde; DBNPA; methylene bisthlocyanate;carbamate; quaternary ammonium compounds; 4,5-dichloro-1,2-dithio-3-one;and 4,5-dichloro-2-N-octyl-4-isothiazolin-3-one, decylthioethylamine,orthophthaldehyde, 2-bromo-2-nitropropane-1,3-diol,4,5-dichloro-1,2-dithiol-3-one, dodecylguanidine hydrochloride,1-(3-chloroallyl)-3,5,7-triaza-1azoniaadamantane chloride, dibromodicyanobutane and bis(trichloromethyl)sulfone.

In an embodiment, the peracetic acid is added prior to the biocide inthe water system. An advantage of the present invention is that itprovides improved compositions for use in inhibiting the growth ofmicroorganisms. Another advantage of the present invention is that itprovides an improved method for inhibiting the growth of microorganisms.

Still further, an advantage of the present invention is that it lowersthe level of expensive chemicals needed for inhibiting the growth ofmicroorganisms. With the addition of a peracetic acid in the watersystem, the non-oxidizing biocide is effective in low dosages, and as aresult is long lasting as evidenced by reductions in microbial growback. The increased effectiveness removes the need for repetitiveadditions of the biocide at multiple points in the paper making system.

Moreover, an advantage of the present invention is that it provides amore cost effective and environmentally friendly method for treatingmicroorganisms.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the detailed description of thepresently preferred embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides, for inhibiting the growth ofmicroorganisms, improved compositions and method of administering thesame to a fluid system. The compositions include a sufficient amount ofa peracetic acid and a non-oxidizing biocide.

The biocide component of this invention includes biocides that exhibit asynergistic effect when added to a fluid stream with a peracetic acid.Examples of suitable non-oxidizing biocides include: isothiazolin;methylene bisthiocyanate; glutaraldehyde; DBNPA; carbamate; quaternaryammonium compounds; 4,5-dichloro 1,2-dithio-3-one; and4,5-dichloro-2-N-octyl-4-isothiazolin-3-one, decylthioethylamine,orthophthaldehyde, 2-bromo-2-nitropropane-1,3-diol,4,5-dichloro-1,2-dithiol-3-one, dodecylguanidine hydrochloride,1-(3-chloroallyl)-3,5,7-triaza-1-azoniaadamantane chloride, dibromodicyanobutane and bis(trichloromethyl)sulfone. Naturally, mixtures ofsuch biocides can also be used.

The biocides can be obtained from a number of chemical suppliers such asAmerican Cyanamid, Buckman, Betz, Dearborn Chemical, EconomicsLaboratory, Inc., Merck, Nalco Chemical Company, and Vineland Chemical.

Peracetic acid may also be obtained from a number of chemical suppliers.One such supplier is FMC Corporation of Philadelphia, Pa.

The combination of a peracetic acid along with such non-oxidizingbiocides provides an unexpected synergistic relationship. Thesynergistic relationship is present in that the cooperative action ofthe combined peracetic acid with the non-oxidizing biocides yields atotal effect which is greater than the sum of the effects of the biocideor the peracetic acid taken separately.

The optimal amounts of biocide and peracetic acid required foreffectiveness in this invention depend on the type of industrial watersbeing treated. In addition, the concentration of the combined componentsvaries greatly and can depend upon the conditions such as temperatureand pH of the waters, and the microbial count. The concentrations may beas little as 1 part per million (ppm) by weight to as much as 250 ppm.With respect to the biocide, the lower and upper limits of the requiredconcentration substantially depend upon the specific biocide orcombination of biocides used.

Still further, since the suitable biocides that may be used in thepresent invention are often obtained at different usable concentrations(i.e. activity level), the ratios vary depending on the particularbiocide combined with the peracetic acid. For example, the peraceticacid used in the examples below is 5% active, the glutaraldehyde is 50%active, and the DBNPA is 20% active. Thus, a 1:1 ratio of PAA:Gluttranslates to 1:10 on an actives basis, while a 1:1 ratio of PAA:DBNPAtranslates to a 1:4 based on actives.

By way of example, and not limitation, the following are biocides,including the percent active of each biocide, that may be used in thepresent invention: isothiazolin (1.5% a.i.); glutaraldehyde (50% a.i.);methylene bisthiocyanate (10% a.i.); DBNPA (20% a.i.); carbamate (30%a.i.); quaternary ammonium compounds (31% a.i.);4,5-dichloro-1,2-dithio-3-one (5% a.i.); and4,5-dichloro-2-N-octyl-4-isothiazolin-3-one (2% a.i.), wherein "a.i."represents active ingredient.

Pursuant to the method of the present invention, the growth ofmicroorganisms in industrial process waters can be inhibited. The methodcomprises the step of adding to the waters the peracetic acid and thenonoxidizing biocide of the present invention. In an embodiment, thebiocide and the peracetic acid are separate components that are added tothe system.

In a preferred embodiment, the peracetic acid is added to the industrialwater prior to the addition of the non-oxidizing biocide. The peraceticacid can be added pursuant to any known method that provides the desiredconcentration of the same in the waters.

After the controlled addition of the peracetic acid, the non-oxidizingbiocide is then added to the water system. In an embodiment, thenon-oxidizing biocide is added 30 minutes after the peracetic acid isadded to the system. Similar to the peracetic acid addition, the biocidecan be added pursuant to any known method that provides the desiredconcentration of the biocide in the waters.

In an embodiment, the method comprises adding approximately 5 to 250 ppmof the non-oxidizing biocide along with approximately 10 to 250 ppm ofthe peracetic acid. In an embodiment, the biocide and the peracetic acidare present in a range from about 1 ppm to 1000 ppm of product.

Peracetic acid is a unique oxidant, utilizing a different mode of actionthan other oxidants. Given the structure of the molecule:

    H.sub.3 COOOH

the hydrocarbon tail allows PAA to penetrate into the bacterial cell.This enables the molecule to disrupt S--S and S--H bonds both inside andoutside of the organisms, killing more quickly and effectively thanother oxidants. Other oxidants, such as HOCl, ClO₂, H₂ O₂, etc. do notpenetrate the cells in this manner because they do not have an organicportion to facilitate entrance into the bacterial cell.

Peracetic acid has always been applied by itself in high concentrations.Because it is also an equilibrium molecule, in that it dissociates backto its starting product after it is diluted, it was never expected to beactive at low concentrations. However, its dissociation rate is muchslower than expected, giving an unexpected synergy with other biocideswhen it is applied at low concentrations (as low as 10 ppm of a 5%product or 0.5 ppm active).

Peracetic acid has been used as a sterilant in the food industry formany years, but is generally used at higher concentrations (10,000 to100,000 ppm). Until recently it has not been used in the paper industryfor the control of microorganisms in the papermachine process water.

By way of example, and not limitation, examples of the invention willnow be given.

EXAMPLES

The following examples illustrate the synergistic relationship obtainedwith the compositions of the present invention.

Synergy is mathematically demonstrated by the industry accepted methoddescribed by S. C. Kull et al. in Allied Microbiology, vol. 9, pages538-541 (1961). As applied to this invention, it is as follows:

Q_(A) =the ppm of active non-oxidizing biocide alone which produces anendpoint.

Q_(B) =the ppm of active peracetic acid alone which produces anendpoint.

Q_(a) =the ppm of active peracetic acid, in combination withnon-oxidizing biocide, which produces an endpoint.

Q_(b) =the ppm of active non-oxidizing biocide, in combination, whichproduces an endpoint. ##EQU1##

The following test procedures were utilized during the experimentationof the present invention.

Process water from several paper mills was obtained for test purposes.Aliquots of water from each mill were dosed with the indicatedconcentrations of peracetic acid (5% active obtained from FMC). After 30minutes of contact time, the designated concentrations of non-oxidizingbiocide were added to the aliquots previously dosed with PAA, mixed welland incubated at 37° C. in and orbital shaker. At the designated contacttimes, each aliquot was sampled to determine the total number of viableorganisms in colony forming units per milliliter (CFU/mL) on TryptoneGlucose Extract (TGE) agar. An endpoint of 2,3,4 or 5 log₁₀ reduction inviable organisms was then selected for calculating synergy.

Example 1

Synergistic activity against microorganisms was demonstrated in millfurnish at pH 7.0.

    ______________________________________    Biocide    (ppm product)    ______________________________________             30 Min.                    90 Min.   5 Hours  24 Hours    ______________________________________    PAA-10     2.3 × 10.sup.6                        4.0 × 10.sup.6                                  2.8 × 10.sup.6                                         6.4 × 10.sup.6    PAA-20     5.8 × 10.sup.5                        9.3 × 10.sup.5                                  2.3 × 10.sup.5                                         6.5 × 10.sup.5    ______________________________________             0 min. 60 min.   4.5 hr.  24 hr.    ______________________________________    Glut-50    3.2 × 10.sup.6                        3.2 × 10.sup.4                                  <10.sup.1                                         <10.sup.1    Glut-30    3.7 × 10.sup.6                        2.5 × 10.sup.5                                  <10.sup.1                                         <10.sup.1    Glut-20    4.2 × 10.sup.6                        7.2 × 10.sup.5                                  2.6 × 10.sup.4                                         1.1 × 10.sup.2    Glut-10    4.4 × 10.sup.6                        2.8 × 10.sup.6                                  2.3 × 10.sup.6                                         9.5 × 10.sup.2    Glut-10/PAA-10               4.5 × 10.sup.6                        3.2 × 10.sup.5                                  5.3 × 10.sup.4                                         1.9 × 10.sup.2    Glut-10/PAA-20               1.2 × 10.sup.5                        5.3 × 10.sup.4                                  2.1 × 10.sup.4                                         3.1 × 10.sup.2    Control-0  2.3 × 10.sup.6                        1.0 × 10.sup.5                                  3.3 × 10.sup.6                                         5.0 × 10.sup.6    ______________________________________

After 90 minutes of contact, a 2 log₁₀ drop is achieved with:

PAA>20 ppm (40 ppm)

Glutaraldehyde=50 ppm

PAA=20 ppm/Glut=10 ppm

SI=10/50+20/40=0.7

After 5 hours of contact, a 2 log₁₀ drop is achieved with:

PAA>20 ppm (40 ppm)

Glutaraldehyde=20 ppm

PAA=10 ppm/glut=10 ppm

SI=10/40+10/20=0.75

After 24 hours of contact, a 4 log₁₀ drop is achieved with:

PAA>20 ppm (40 ppm)

Glutaraldehyde=20 ppm

PAA=10 ppm/glut=10 ppm

SI=10/40+10/20=0.75

Example 2

    ______________________________________    Biocide    (ppm product)    ______________________________________              30 Min.                     90 Min.   5 Hours  24 Hours    ______________________________________    PAA-5       7.4 × 10.sup.5                         8.5 × 10.sup.5                                   7.8 × 10.sup.5                                          8.8 × 10.sup.6    PAA-10      6.4 × 10.sup.5                         6.7 × 10.sup.5                                   5.2 × 10.sup.5                                          2.9 × 10.sup.6    PAA-20      4.0 × 10.sup.5                         5.4 × 10.sup.5                                   1.0 × 10.sup.5                                          5.1 × 10.sup.5    ______________________________________              0 min. 60 min.   4.5 hr.  24 hr.    ______________________________________    DBNPA-100   3.9 × 10.sup.5                         <10.sup.1 <10.sup.1                                          <10.sup.1    DBNPA-75    5.1 × 10.sup.5                         <10.sup.1 <10.sup.1                                          <10.sup.1    DBNPA-50    6.0 × 10.sup.5                         8.1 × 10.sup.2                                   <10.sup.1                                          <10.sup.1    DBNPA-25    6.0 × 10.sup.5                         3.3 × 10.sup.3                                   <10.sup.1                                          9.4 × 10.sup.4    DBNPA-100/PAA-5                4.3 × 10.sup.5                         <10.sup.1 <10.sup.1                                          <10.sup.1    DBNPA-75/PAA-5                6.1 × 10.sup.5                         <10.sup.1 <10.sup.1                                          <10.sup.1    DBNPA-50/PAA-5                3.7 × 10.sup.5                         <10.sup.1 <10.sup.1                                          <10.sup.1    DBNPA-25/PAA-5                8.8 × 10.sup.5                         3.4 × 10.sup.3                                   1.1 × 10.sup.2                                          <10.sup.1    DBNPA-100/PAA-10                5.5 × 10.sup.5                         <10.sup.1 <10.sup.1                                          <10.sup.1    DBNPA-75/PAA-10                1.4 × 10.sup.5                         <10.sup.1 <10.sup.1                                          <10.sup.1    DBNPA-50/PAA-10                9.5 × 10.sup.4                         <10.sup.1 <10.sup.1                                          <10.sup.1    DBNPA-25/PAA-10                3.6 × 10.sup.4                         <10.sup.1 <10.sup.1                                          <10.sup.1    DBNPA-100/PAA-20                2.0 × 10.sup.5                         <10.sup.1 <10.sup.1                                          <10.sup.1    DBNPA-75/PAA-20                5.4 × 10.sup.5                         <10.sup.1 <10.sup.1                                          <10.sup.1    DBNPA-50/PAA-20                4.5 × 10.sup.5                         <10.sup.1 <10.sup.1                                          <10.sup.1    DBNPA-25/PAA-20                3.7 × 10.sup.5                         <10.sup.1 <10.sup.1                                          <10.sup.1    Control-0   3.7 × 10.sup.5                         9.0 × 10.sup.5                                   3.0 × 10.sup.5                                          2.4 × 10.sup.6    ______________________________________

After 90 minutes of contact, a 5 log₁₀ drop is achieved with:

PAA>20 ppm (40 ppm)

DBNPA=75 ppm

PAA=5 ppm/DBNPA=50 ppm

SI=5/40+50/75=0.79

PAA=10 ppm/DBNPA=25 ppm

SI=10/40+25/75=0.58

After 24 hours of contact, a 5 log₁₀ drop is achieved with:

PAA>20 ppm (40 ppm)

DBNPA=50 ppm

PAA=5 ppm/DBNPA=25 ppm

SI=5/40+25/50=0.625

Example 3

Synergistic activity against microorganisms was demonstrated in millfurnish at pH 7.1.

    ______________________________________    Biocide    (ppm product)    ______________________________________             30 Min.                    2 Hours   5 Hours  24 Hours    ______________________________________    PAA-25     2.2 × 10.sup.6                        1.4 × 10.sup.6                                  2.9 × 10.sup.6                                         7.3 × 10.sup.6    PAA-50     2.9 × 10.sup.4                        7.5 × 10.sup.4                                  2.1 × 10.sup.4                                         1.8 × 10.sup.6    PAA-100    6.8 × 10.sup.2                        6.1 × 10.sup.2                                  5.9 × 10.sup.2                                         2.4 × 10.sup.6    ______________________________________             0 Min. 1.5 Hrs.  4.5 Hrs. 24 Hrs.    ______________________________________    MBT-5               9.8 × 10.sup.6                                  7.1 × 10.sup.6                                         1.6 × 10.sup.6    MBT-10              3.6 × 10.sup.6                                  5.7 × 10.sup.6                                         3.8 × 10.sup.6    MBT-25              2.4 × 10.sup.6                                  8.0 × 10.sup.5                                         7.5 × 10.sup.6    MBT-50     2.2 × 10.sup.6                        2.1 × 10.sup.6                                  2.1 × 10.sup.5                                         3.4 × 10.sup.5    PAA-10/MBT-5        3.8 × 10.sup.6                                  7.7 × 10.sup.6                                         4.6 × 10.sup.7    PAA-10/MBT-10       4.3 × 10.sup.6                                  5.2 × 10.sup.6                                         4.5 × 10.sup.7    PAA-10/MBT-25       1.9 × 10.sup.6                                  2.6 × 10.sup.6                                         1.1 × 10.sup.7    PAA-10/MBT-50               3.8 × 10.sup.6                        1.7 × 10.sup.6                                  3.4 × 10.sup.5                                         7.7 × 10.sup.4    PAA-20/MBT-5        1.4 × 10.sup.6                                  2.1 × 10.sup.6                                         1.8 × 10.sup.7    PAA-20/MBT-10       1.9 × 10.sup.6                                  1.1 × 10.sup.6                                         1.6 × 10.sup.7    PAA-20/MBT-25       1.1 × 10.sup.5                                  4.6 × 10.sup.5                                         3.3 × 10.sup.6    PAA-20/MBT-50               1.7 × 10.sup.6                        6.0 × 10.sup.5                                  6.3 × 10.sup.4                                         2.4 × 10.sup.3    PAA-40/MBT-5        8.2 × 10.sup.4                                  2.8 × 10.sup.4                                         1.2 × 10.sup.7    PAA-40/MBT-10       9.2 × 10.sup.4                                  2.5 × 10.sup.4                                         1.3 × 10.sup.7    PAA-40/MBT-25       6.3 × 10.sup.4                                  1.6 × 10.sup.4                                         4.0 × 10.sup.5    PAA-40/MBT-50               1.4 × 10.sup.5                        4.9 × 10.sup.4                                  2.2 × 10.sup.4                                         1.8 × 10.sup.3    Control-0  1.1 × 10.sup.7                        1.5 × 10.sup.7                                  3.1 × 10.sup.7                                         7.5 × 10.sup.3    ______________________________________

After 24 hours of contact, a 3 log₁₀ drop is achieved with:

PAA>100 ppm (200 ppm)

MBT>50 ppm (100 ppm)

PAA=20 ppm/MBT=50 ppm

SI=20/200+50/100=0.6

After 5 hours of contact, a 3 log₁₀ drop is achieved with:

PAA>50 ppm

MBT>50 ppm (100 ppm)

PAA=20 ppm/MBT=50 ppm

SI=20/50+50/100=0.9

Example 4

Synergistic activity against microorganisms was demonstrated in millfurnish at pH 7.28.

    ______________________________________    Biocide    (ppm product)    ______________________________________              30 Min.                     2 Hours   5 Hours  24 Hours    ______________________________________    PAA-25      1.3 × 10.sup.5                         2.4 × 10.sup.5                                   1.8 × 10.sup.6                                          3.0 × 10.sup.7    PAA-50      1.6 × 10.sup.3                         2.5 × 10.sup.3                                   1.0 × 10.sup.4                                          1.7 × 10.sup.7    PAA-100     1.3 × 10.sup.2                         1.5 × 10.sup.3                                   1.5 × 10.sup.3                                          8.1 × 10.sup.6    ______________________________________              0 Min. 1.5 Hr.   4.5 Hr.  24 Hr.    ______________________________________    CARB-50              9.8 × 10.sup.6                                   1.1 × 10.sup.7                                          2.6 × 10.sup.6    CARB-100             9.4 × 10.sup.6                                   7.2 × 10.sup.6                                          7.8 × 10.sup.4    CARB-150             1.1 × 10.sup.6                                   1.0 × 10.sup.6                                          3.8 × 10.sup.4    CARB-200    4.7 × 10.sup.6                         1.8 × 10.sup.6                                   1.0 × 10.sup.6                                          3.0 × 10.sup.4    PAA-10/CARB-50       2.8 × 10.sup.6                                   2.5 × 10.sup.6                                          2.8 × 10.sup.4    PAA-10/CARB-100      3.2 × 10.sup.6                                   5.0 × 10.sup.4                                          4.0 × 10.sup.4    PAA-10/CARB-150      3.0 × 10.sup.6                                   2.6 × 10.sup.4                                          4.8 × 10.sup.4    PAA-10/CARB-200                2.2 × 10.sup.6                         1.4 × 10.sup.5                                   5.9 × 10.sup.4                                          2.5 × 10.sup.3    PAA-20/CARB-50       1.1 × 10.sup.5                                   2.0 × 10.sup.6                                          2.1 × 10.sup.3    PAA-20/CARB-100      3.9 × 10.sup.4                                   4.5 × 10.sup.4                                          1.2 × 10.sup.3    PAA-20/CARB-150      2.3 × 10.sup.4                                   2.5 × 10.sup.4                                          1.5 × 10.sup.3    PAA-20/CARB-200                3.7 × 10.sup.5                         2.5 × 10.sup.4                                   1.9 × 10.sup.4                                          8.1 × 10.sup.2    PAA-40/CARB-50       2.3 × 10.sup.3                                   1.2 × 10.sup.3                                          9.3 × 10.sup.2    PAA-40/CARB-100      2.0 × 10.sup.3                                   7.0 × 10.sup.2                                          5.4 × 10.sup.2    PAA-40/CARB-150      1.4 × 10.sup.3                                   6.6 × 10.sup.2                                          6.8 × 10.sup.2    PAA-40/CARB-200                1.0 × 10.sup.4                         1.3 × 10.sup.3                                   5.6 × 10.sup.2                                          6.0 × 10.sup.2    Control-0   1.2 × 10.sup.7                         3.0 × 10.sup.6                                   3.0 × 10.sup.6                                          3.2 × 10.sup.7    ______________________________________

After 2 hours of contact, a 2 log₁₀ drop was achieved with:

PAA=50 ppm

CARB>200 ppm (400 ppm)

PAA=20 ppm/CARB=100 ppm

SI=20/50+100/400=0.65

PAA=40 ppm/CARB<50 ppm

SI=40/50+25/400=0.8625

After 5 hours of contact, a 4 log₁₀ drop was achieved with:

PAA>100 ppm (200 ppm)

CARB>200 ppm (400 ppm)

PAA=40 ppm/CARB=100 ppm

SI=40/200+100/400=0.45

After 24 hours of contact, a 4 log₁₀ drop was achieved with:

PAA>100 ppm (200 ppm)

CARB>200 ppm (400 ppm)

PAA=10 ppm/CARB=200 ppm

SI=10/200+200/400=0.55

PAA=20 ppm/CARB=50 ppm

SI=20/200+50/400=0.225

PAA=40 ppm/CARB=50 ppm

SI=40/200+50/400=0.325

Example 5

    ______________________________________    Biocide    (ppm product)    ______________________________________              30 Min.                     3 Hours   5 Hours  24 Hours    ______________________________________    PAA-25      4.2 × 10.sup.6                         5.4 × 10.sup.6                                   5.3 × 10.sup.6                                          1.7 × 10.sup.7    PAA-50      4.4 × 10.sup.4                         1.1 × 10.sup.5                                   7.3 × 10.sup.4                                          1.9 × 10.sup.7    PAA-100     8.0 × 10.sup.2                         1.1 × 10.sup.3                                   1.1 × 10.sup.3                                          1.3 × 10.sup.7    ______________________________________              0 Min. 2.5 Hr.   4.5 Hr.  24 Hr.    ______________________________________    QUAT-25              2.7 × 10.sup.5                                   3.0 × 10.sup.5                                          1.8 × 10.sup.7    QUAT-50              1.0 × 10.sup.5                                   1.7 × 10.sup.5                                          1.1 × 10.sup.7    QUAT-100             7.9 × 10.sup.4                                   8.6 × 10.sup.4                                          5.2 × 10.sup.6    QUAT-200    7.5 × 10.sup.4                         6.4 × 10.sup.2                                   7.2 × 10.sup.2                                          1.6 × 10.sup.2    PAA-10/QUAT-25       1.2 × 10.sup.5                                   2.0 × 10.sup.5                                          1.7 × 10.sup.7    PAA-10/QUAT-50       6.6 × 10.sup.4                                   1.3 × 10.sup.5                                          7.3 × 10.sup.6    PAA-10/QUAT-100      1.3 × 10.sup.3                                   3.1 × 10.sup.3                                          1.6 × 10.sup.7    PAA-10/QUAT-200                1.7 × 10.sup.5                         5.0 × 10.sup.2                                   6.8 × 10.sup.2                                          2.9 × 10.sup.6    PAA-20/QUAT-25       1.8 × 10.sup.5                                   1.2 × 10.sup.5                                          4.9 × 10.sup.6    PAA-20/QUAT-50       9.1 × 10.sup.4                                   1.2 × 10.sup.5                                          6.5 × 10.sup.6    PAA-20/QUAT-100      3.9 × 10.sup.3                                   6.8 × 10.sup.3                                          5.0 × 10.sup.6    PAA-20/QUAT-200                6.3 × 10.sup.4                         5.4 × 10.sup.2                                   6.6 × 10.sup.2                                          2.4 × 10.sup.2    PAA-40/QUAT-25       3.4 × 10.sup.3                                   4.0 × 10.sup.3                                          8.9 × 10.sup.6    PAA-40/QUAT-50       1.9 × 10.sup.3                                   1.7 × 10.sup.3                                          3.0 × 10.sup.5    PAA-40/QUAT-100      2.0 × 10.sup.3                                   1.7 × 10.sup.3                                          4.0 × 10.sup.5    PAA-40/QUAT-200                1.3 × 10.sup.3                         3.7 × 10.sup.2                                   5.3 × 10.sup.2                                          1.9 × 10.sup.2    Control-0   1.1 × 10.sup.7                         1.4 × 10.sup.7                                   1.3 × 10.sup.7                                          2.1 × 10.sup.7    ______________________________________

After 24 hours of contact, a 2 log₁₀ drop was achieved with:

PAA>100 ppm (200 ppm)

QUAT=200 ppm

PAA=40 ppm/QUAT=50 ppm

SI=40/200+50/200=0.45

After 3 hours & 5 hours of contact, a 4 log₁₀ drop was achieved with:

PAA=100 ppm

QUAT=200 ppm

PAA=40 ppm/QUAT=25 ppm

SI=40/100+25/200=0.525

Example 6

Synergistic activity against microorganisms was demonstrated in millfurnish at pH 7.5.

    ______________________________________    Biocide    (ppm product)    ______________________________________             30 Min. 90 Min.  5 Hours   24 Hours    ______________________________________    PAA-10     4.9 × 10.sup.5                         5.0 × 10.sup.5                                  2.5 × 10.sup.6                                          9.6 × 10.sup.6    PAA-25     2.9 × 10.sup.5                         4.8 × 10.sup.5                                  4.2 × 10.sup.6                                          2.3 × 10.sup.6    PAA-50     6.3 × 10.sup.4                         1.8 × 10.sup.5                                  4.1 × 10.sup.5                                          2.5 × 10.sup.7    ______________________________________             0 Min.  60 Min.  4.5 Hr.   24 Hr.    ______________________________________    ISO-133    7.4 × 10.sup.5                         5.1 × 10.sup.5                                  4.7 × 10.sup.5                                          1.6 × 10.sup.4    ISO-100    7.3 × 10.sup.5                         5.6 × 10.sup.5                                  4.2 × 10.sup.5                                          1.9 × 10.sup.4    ISO-67     7.8 × 10.sup.5                         5.9 × 10.sup.5                                  3.8 × 10.sup.5                                          9.6 × 10.sup.4    ISO-33     8.0 × 10.sup.5                         5.7 × 10.sup.5                                  6.1 × 10.sup.5                                          2.2 × 10.sup.7    PAA-10/ISO-133               5.2 × 10.sup.5                         1.6 × 10.sup.5                                  2.1 × 10.sup.5                                          1.1 × 10.sup.4    PAA-10/ISO-100               3.1 × 10.sup.5                         1.4 × 10.sup.5                                  3.4 × 10.sup.5                                          2.1 × 10.sup.4    PAA-10/ISO-67               3.7 × 10.sup.5                         2.1 × 10.sup.5                                  4.8 × 10.sup.5                                          4.9 × 10.sup.4    PAA-10/ISO-33               2.6 × 10.sup.5                         2.2 × 10.sup.5                                  6.4 × 10.sup.5                                          5.3 × 10.sup.6    PAA-25/ISO-133               1.4 × 10.sup.5                         6.7 × 10.sup.4                                  1.1 × 10.sup.5                                          3.2 × 10.sup.3    PAA-25/ISO-100               1.6 × 10.sup.5                         8.7 × 10.sup.4                                  1.2 × 10.sup.5                                          4.2 × 10.sup.3    PAA-25/ISO-67               .sup.  1.2 × 10.sup.5+                         8.0 × 10.sup.4                                  1.4 × 10.sup.5                                          4.9 × 10.sup.3    PAA-25/ISO-133               1.5 × 10.sup.5                         9.4 × 10.sup.4                                  1.6 × 10.sup.5                                          9.8 × 10.sup.5    PAA-50/ISO-133               1.8 × 10.sup.4                         5.5 × 10.sup.3                                  5.3 × 10.sup.3                                          1.6 × 10.sup.2    PAA-50/ISO-100               1.4 × 10.sup.4                         6.8 × 10.sup.3                                  3.5 × 10.sup.4                                          3.2 × 10.sup.2    PAA-50/ISO-67               3.3 × 10.sup.4                         1.2 × 10.sup.4                                  3.3 × 10.sup.4                                          1.1 × 10.sup.3    PAA-50/ISO-33               1.9 × 10.sup.4                         2.3 × 10.sup.4                                  5.1 × 10.sup.4                                          5.4 × 10.sup.3    Control-0  8.2 × 10.sup.5                         7.1 × 10.sup.5                                  2.5 × 10.sup.6                                          4.3 × 10.sup.6    ______________________________________

After 90 minutes of contact, a 1 log₁₀ drop was achieved with:

PAA>50 ppm (100 ppm)

ISO>133 ppm (167 ppm)

PAA=25 ppm/ISO=67 ppm

SI=25/100+67/167=0.65

After 5 hours of contact, a 2 log₁₀ drop was achieved with:

PAA>50 ppm (100 ppm)

ISO>133 ppm (167 ppm)

PAA>50 ppm/ISO=33 ppm

SI=50/100+33/167=0.70

After 24 hours of contact, a 3 log₁₀ drop was achieved with:

PAA>50 ppm (100 ppm)

ISO>133 ppm (167 ppm)

PAA=25 ppm/ISO=67 ppm

SI=25/100+67/167=0.65

Example 7

Trials were conducted at a paper mill where inadequate antimicrobialcontrol was being applied and slime began to develop on machinesurfaces. The aerobic bacterial population on the machine surfaces wasfound to persist at 1×10⁷ CFU/mL. At counts higher than this, the millexperiences sever slime problems and the quality of paper being producedis compromised.

If a 1.5% isothiazolin blend is fed to this machine as a sole biocide,150 ppm of the 1.5% isothiazolin blend is needed to hold the populationto 5×10⁶ CFU/mL. However, over an extended period of time, even thishigh dosage becomes inadequate. A combination of 10 ppm of a 4.5%peracetic acid solution and 17 ppm of the 1.5% isothiazolin blendallowed the counts to increase to the level of 1×10⁷ CFU/mL. Byincreasing the 1.5% isothiazolin blend to 33 ppm, the population droppedto 1×10⁴ CFU/mL.

Laboratory testing has shown that a 50 ppm dose of the 4.5% peraceticacid solution is needed to drop the population to 10⁴ CFU/mL by itself.Using this information, a synergy index can be calculated:

To achieve a 3 log drop:

alone 4.5% peracetic acid solution=50 ppm

alone 1.5% isothiazolin blend>150 ppm (200 ppm) or

Combination of 10 ppm 4.5% peracetic acid solution+33 ppm of N-7647Synergy Index

10/50+33/200=0.365

The 4.5% peracetic acid solution was being fed continuously to thewhitewater loop and the 1.5% isothiazolin blend was being fedintermittently to the same application point. On an actives basis, whenthe 1.5% isothiazolin blend was being added, this ratio is very close to1:1. This range will vary, mill to mill, anywhere from 5:1 to 1:5 forthis combination. Based on the laboratory data, ratios for other biocidecombinations would be expected to range from 1:1 to 1:200, on an activesbasis.

The present invention lowers the levels of expensive chemicals neededfor inhibiting the growth of microorganisms. As illustrated in thefigure, a 100 ppm dosage of biocide, such as carbamate, in combinationwith 20 ppm dosage of peracetic acid is more effective thanadministering either 25 ppm of peracetic acid or 200 ppm of the biocidealone. Accordingly, the present invention provides a more cost effectiveand environmentally friendly method for treating microorganisms.

Example 8

In an attempt to demonstrate synergistic activity of peracetic acid andbromohydroxyacetophenone (BHAP) against microorganisms found in papermill whitewater, pH 7.1, the following experiment was performed.However, instead of synergistic activity, it was found that these 2biocides are antagonistic. Although this was not the intended result,this experiment shows that peracetic acid is not synergistic with allorganic biocides.

    ______________________________________    Biocide    (ppm product)    ______________________________________               60 min   300 min  24 Hours    ______________________________________    PAA-25       2.9 × 10.sup.6                            1.7 × 10.sup.7                                     2.7 × 10.sup.7    PAA-50       1.5 × 10.sup.6                            4.7 × 10.sup.6                                     4.0 × 10.sup.7    PAA-100      1.1 × 10.sup.6                            1.6 × 10.sup.5                                     6.5 × 10.sup.7    ______________________________________               30 min   270 min  24 Hours    ______________________________________    BHAP-12.5    2.4 × 10.sup.6                            9.8 × 10.sup.4                                     4.5 × 10.sup.7    BHAP-25      1.4 × 10.sup.6                            2.7 × 10.sup.4                                     1.7 × 10.sup.7    BHAP-50      6.0 × 10.sup.5                            6.2 × 10.sup.4                                     1.0 × 10.sup.3    BHAP-100     4.2 × 10.sup.5                            1.3 × 10.sup.4                                     1.5 × 10.sup.2    PAA-10/BHAP-12.5                 3.9 × 10.sup.6                            6.0 × 10.sup.5                                     4.9 × 10.sup.7    PAA-10/BHAP-25                 2.7 × 10.sup.6                            1.9 × 10.sup.5                                     1.9 × 10.sup.7    PAA-10/BHAP-50                 1.0 × 10.sup.6                            8.5 × 10.sup.4                                     1.8 × 10.sup.7    PAA-10/BHAP-100                 2.0 × 10.sup.6                            1.1 × 10.sup.5                                     9.7 × 10.sup.2    PAA-20/BHAP-12.5                 3.6 × 10.sup.6                            1.2 × 10.sup.6                                     4.1 × 10.sup.7    PAA-20/BHAP-25                 2.0 × 10.sup.6                            7.0 × 10.sup.5                                     1.6 × 10.sup.7    PAA-20/BHAP-50                 1.8 × 10.sup.6                            8.7 × 10.sup.4                                     8.2 × 10.sup.4    PAA-20/BHAP-100                 1.4 × 10.sup.6                            5.3 × 10.sup.4                                     3.2 × 10.sup.2    PAA-40/BHAP-12.5                 1.5 × 10.sup.6                            1.9 × 10.sup.6                                     4.8 × 10.sup.7    PAA-40/BHAP-25                 1.8 × 10.sup.6                            7.1 × 10.sup.4                                     2.6 × 10.sup.7    PAA-40/BHAP-50                 1.4 × 10.sup.6                            9.0 × 10.sup.4                                     2.0 × 10.sup.5    PAA-40/BHAP-100                 9.0 × 10.sup.5                            6.7 × 10.sup.4                                     3.0 × 10.sup.2    Control - 0  7.1 × 10.sup.6                            6.0 × 10.sup.6                                     1.0 × 10.sup.7    ______________________________________

Synergy Calculation:

For a 4 log₁₀ reduction after 24 hours contact:

PAA=>100 (200)

BHAP=50

PAA/BHAP=10/100 10/200+100/50=2.05=SI

Example 9

Synergistic activity of peracetic acid and dibromo dicyanobutane (DBDCB)against microorganisms was demonstrated in paper mill process water atpH 7.0.

    ______________________________________    Biocide    (ppm product)    ______________________________________                60 min   300 min  24 Hours    ______________________________________    PAA-25        3.3 × 10.sup.6                             1.1 × 10.sup.7                                      1.3 × 10.sup.7    PAA-50        6.4 × 10.sup.5                             5.6 × 10.sup.6                                      3.4 × 10.sup.7    PAA-100       2.7 × 10.sup.5                             1.6 × 10.sup.4                                      3.0 × 10.sup.7    ______________________________________                30 min   270 min  24 Hours    ______________________________________    DBDCB-25      2.1 × 10.sup.6                             8.1 × 10.sup.4                                      4.5 × 10.sup.6    DBDCB-50      2.2 × 10.sup.6                             1.1 × 10.sup.3                                      1.8 × 10.sup.2    DBDCB-100     3.6 × 10.sup.6                             2.0 × 10.sup.3                                      <10.sup.1    DBDCB-200     2.8 × 10.sup.6                             9.7 × 10.sup.2                                      <10.sup.1    PAA-10/DBDCB-25                  3.9 × 10.sup.6                             1.1 × 10.sup.5                                      6.5 × 10.sup.2    PAA-10/DBDCB-50                  3.1 × 10.sup.6                             8.2 × 10.sup.3                                      4.3 × 10.sup.2    PAA-10/DBDCB-100                  1.9 × 10.sup.6                             2.9 × 10.sup.3                                      <10.sup.1    PAA-10/DBDCB-200                  3.7 × 10.sup.6                             3.7 × 10.sup.3                                      <10.sup.1    PAA-20/DBDCB-25                  2.6 × 10.sup.6                             3.4 × 10.sup.5                                      2.9 × 10.sup.3    PAA-20/DBDCB-50                  2.1 × 10.sup.6                             1.3 × 10.sup.3                                      2.1 × 10.sup.2    PAA-20/DBDCB-100                  1.8 × 10.sup.6                             7.0 × 10.sup.3                                      4.8 × 10.sup.1    PAA-20/DBDCB-200                  3.7 × 10.sup.6                             3.7 × 10.sup.3                                      2.1 × 10.sup.1    PAA-40/DBDCB-25                  1.7 × 10.sup.6                             2.9 × 10.sup.4                                      6.8 × 10.sup.2    PAA-40/DBDCB-50                  1.7 × 10.sup.6                             9.1 × 10.sup.3                                      4.1 × 10.sup.2    PAA-40/DBDCB-100                  3.3 × 10.sup.5                             2.4 × 10.sup.3                                      1.3 × 10.sup.1    PAA-40/DBDCB-200                  2.4 × 10.sup.5                             2.3 × 10.sup.3                                      <10.sup.1    Control - 0   5.5 × 10.sup.6                             6.6 × 10.sup.6                                      7.4 × 10.sup.6    ______________________________________

Synergy Calculation:

For a 4 ₁₀ log reduction after 24 hours contact:

PAA=>100 (200)

DBDCB=50

PAA/DBDCB=10/25 10/200+25/50=0.55=SI

Example 10

When attempting to demonstrate the synergistic activity of peraceticacid and dodecyl guanidine hydrochloride against bacteria found in papermill whitewater at pH 7.1, it was discovered that synergy occurs withthese chemicals after 1 hour of exposure, but their effects areantagonistic after 24 hours of static exposure. This experimentdemonstrates the importance of feeding the chemicals at the correctintervals to ensure the desired result.

    ______________________________________    Biocide    (ppm product)    ______________________________________              60 min   300 min  24 Hours    ______________________________________    PAA-25      3.8 × 10.sup.5                           4.6 × 10.sup.6                                    4.3 × 10.sup.7    PAA-50      2.5 × 10.sup.5                           4.5 × 10.sup.6                                    2.7 × 10.sup.7    PAA-100     1.9 × 10.sup.5                           2.0 × 10.sup.4                                    2.1 × 10.sup.7    ______________________________________              30 min   270 min  24 Hours    ______________________________________    DGH-10      3.6 × 10.sup.5                           3.2 × 10.sup.6                                    2.4 × 10.sup.7    DGH-20      3.3 × 10.sup.5                           4.3 × 10.sup.5                                    3.0 × 10.sup.7    DGH-40      5.4 × 10.sup.4                           7.6 × 10.sup.2                                    6.1 × 10.sup.4    DGH-80      2.7 × 10.sup.2                           <10.sup.1                                    2.8 × 10.sup.2    PAA-10/DGH-10                4.6 × 10.sup.5                           4.0 × 10.sup.6                                    2.3 × 10.sup.7    PAA-10/DGH-20                1.7 × 10.sup.5                           1.2 × 10.sup.5                                    1.9 × 10.sup.7    PAA-10/DGH-40                2.4 × 10.sup.3                           8.2 × 10.sup.2                                    2.7 × 10.sup.4    PAA-10/DGH-80                2.5 × 10.sup.2                           <10.sup.1                                    4.6 × 10.sup.2    PAA-20/DGH-10                4.9 × 10.sup.5                           3.7 × 10.sup.6                                    1.9 × 10.sup.7    PAA-20/DGH-20                3.4 × 10.sup.5                           3.2 × 10.sup.5                                    1.8 × 10.sup.7    PAA-20/DGH-40                1.6 × 10.sup.3                           2.9 × 10.sup.3                                    2.0 × 10.sup.7    PAA-20/DGH-80                3.5 × 10.sup.2                           2.8 × 10.sup.1                                    2.3 × 10.sup.5    PAA-40/DGH-10                1.9 × 10.sup.5                           9.8 × 10.sup.5                                    2.1 × 10.sup.7    PAA-40/DGH-20                3.2 × 10.sup.5                           1.2 × 10.sup.6                                    1.6 × 10.sup.7    PAA-40/DGH-40                1.6 × 10.sup.2                           2.8 × 10.sup.2                                    1.5 × 10.sup.7    PAA-40/DGH-80                1.6 × 10.sup.2                           1.9 × 10.sup.1                                    2.0 × 10.sup.7    Control - 0 5.5 × 10.sup.6                           6.6 × 10.sup.6                                    7.4 × 10.sup.6    ______________________________________

Synergy Calculation:

For a 3 ₁₀ log reduction after 1 hours contact:

PAA=>100 (200)

DGH=80

PAA/DGH=40/40 40/200+40/80=0.7=SI Synergy

For a 5 log₁₀ reduction after 24 hours of contact:

PAA=>100 (200)

DGH=80

PAA/DGH=40(80)/>80(160) 80/200+160/80=2.4=SI Antagonism

Example 11

Synergistic activity of peracetic acid and dodecylthioethylamine (DTEA)against microorganisms was demonstrated in paper mill whitewater, pH7.1.

    ______________________________________    Biocide    (ppm product)    ______________________________________               60 min    300 min  24 Hours    ______________________________________    PAA-20       6.5 × 10.sup.5                             2.9 × 10.sup.6                                      8.4 × 10.sup.6    PAA-40       8.7 × 10.sup.4                             7.0 × 10.sup.4                                      3.1 × 10.sup.7    PAA-80       1.3 × 10.sup.4                             2.9 × 10.sup.3                                      1.8 × 10.sup.7    ______________________________________               30 min    270 min  24 Hours    ______________________________________    DTEA-12.5    1.0 × 10.sup.7                             1.1 × 10.sup.7                                      1.5 × 10.sup.7    DTEA-25      1.2 × 10.sup.7                             1.1 × 10.sup.7                                      1.5 × 10.sup.7    DTEA-50      1.2 × 10.sup.7                             9.5 × 10.sup.6                                      1.8 × 10.sup.7    DTEA-100     5.0 × 10.sup.6                             1.1 × 10.sup.6                                      3.2 × 10.sup.7    PAA-10/DTEA-12.5                 3.0 × 10.sup.6                             7.5 × 10.sup.6                                      1.9 × 10.sup.7    PAA-10/DTEA-25                 3.5 × 10.sup.6                             8.6 × 10.sup.6                                      1.8 × 10.sup.7    PAA-10/DTEA-50                 2.7 × 10.sup.6                             4.8 × 10.sup.6                                      3.0 × 10.sup.7    PAA-10/DTEA-100                 1.1 × 10.sup.2                             5.0 × 10.sup.5                                      3.4 × 10.sup.7    PAA-20/DTEA-12.5                 6.3 × 10.sup.5                             2.1 × 10.sup.6                                      2.0 × 10.sup.7    PAA-20/DTEA-25                 7.1 × 10.sup.5                             1.8 × 10.sup.6                                      2.7 × 10.sup.7    PAA-20/DTEA-50                 6.3 × 10.sup.5                             7.5 × 10.sup.5                                      1.7 × 10.sup.7    PAA-20/DTEA-100                 2.3 × 10.sup.5                             8.9 × 10.sup.4                                      3.1 × 10.sup.7    PAA-40/DTEA-12.5                 3.8 × 10.sup.3                             7.3 × 10.sup.3                                      3.1 × 10.sup.7    PAA-40/DTEA-25                 5.2 × 10.sup.3                             5.2 × 10.sup.2                                      2.4 × 10.sup.7    PAA-40/DTEA-50                 4.7 × 10.sup.3                             4.8 × 10.sup.3                                      3.6 × 10.sup.7    PAA-40/DTEA-100                 2.5 × 10.sup.3                             2.0 × 10.sup.3                                      3.7 × 10.sup.7    Control - 0  1.6 × 10.sup.7                             1.8 × 10.sup.7                                      1.2 × 10.sup.7    ______________________________________

Synergy Calculation:

For a 4 log₁₀ reduction after 1 hours contact:

PAA=>80 (160)

DTEA=100 (200)

PAA/DTEA=40/12.5 40/160+12.50/200=0.3125=SI

For a 4 log₁₀ reduction after 5 hours of contact:

PAA=80

DTEA=>100 (200)

PAA/DTEA=40/12.5 40/80+12.5/200=0.5625=SI

Example 12

Synergistic activity of peracetic acid and orthophthaldehyde (OPA)against microorganisms in paper mill service water, pH 7.0.

    ______________________________________    Biocide    (ppm product)    ______________________________________               150 min   270 min  24 Hours    ______________________________________    PAA-40       2.3 × 10.sup.7                             2.6 × 10.sup.7                                      1.5 × 10.sup.7    PAA-80       1.2 × 10.sup.7                             1.3 × 10.sup.7                                      1.5 × 10.sup.7    PAA-160      4.2 × 10.sup.6                             3.8 × 10.sup.7                                      1.7 × 10.sup.7    ______________________________________               120 min   240 min  24 Hours    ______________________________________    OPA-12.5     2.5 × 10.sup.6                             6.2 × 10.sup.5                                      2.8 × 10.sup.7    OPA-25       2.7 × 10.sup.5                             2.1 × 10.sup.5                                      1.7 × 10.sup.7    OPA-50       4.3 × 10.sup.4                             1.8 × 10.sup.4                                      6.4 × 10.sup.6    OPA-100      1.5 × 10.sup.3                             9.5 × 10.sup.2                                      3.4 × 10.sup.4    PAA-20/OPA-12.5                 4.1 × 10.sup.5                             2.1 × 10.sup.6                                      2.7 × 10.sup.7    PAA-20/OPA-25                 9.7 × 10.sup.4                             1.3 × 10.sup.5                                      1.9 × 10.sup.7    PAA-20/OPA-50                 2.1 × 10.sup.3                             1.8 × 10.sup.3                                      7.1 × 10.sup.6    PAA-20/OPA-100                 7.2 × 10.sup.2                             <10.sup.1                                      4.8 × 10.sup.5    PAA-40/OPA-12.5                 3.0 × 10.sup.5                             2.0 × 10.sup.5                                      1.5 × 10.sup.7    PAA-40/OPA-25                 5.4 × 10.sup.4                             8.9 × 10.sup.3                                      5.2 × 10.sup.6    PAA-40/OPA-50                 9.2 × 10.sup.2                             7.4 × 10.sup.2                                      1.5 × 10.sup.7    PAA-40/OPA-100                 6.4 × 10.sup.7                             6.2 × 10.sup.2                                      5.3 × 10.sup.5    PAA-80/OPA-12.5                 2.4 × 10.sup.5                             1.7 × 10.sup.3                                      1.8 × 10.sup.7    PAA-80/OPA-25                 3.1 × 10.sup.3                             4.4 × 10.sup.2                                      3.1 × 10.sup.6    PAA-80/OPA-50                 6.1 × 10.sup.2                             6.7 × 10.sup.2                                      4.6 × 10.sup.3    PAA-80/OPA-100                 7.4 × 10.sup.2                             5.3 × 10.sup.2                                      3.5 × 10.sup.3    Control - 0  2.5 × 10.sup.7                             3.1 × 10.sup.7                                      1.3 × 10.sup.7    ______________________________________

Synergy Calculation:

For a 4 log₁₀ reduction after 24 hours contact:

PAA=>160 (320)

OPA=>100 (200)

PAA/OPA=80/50 80/320+50/200=0.5=SI

For a 4 log₁₀ reduction after 5 hours of contact:

PAA=>160 (320)

OPA=100

PAA/OPA=80/12.5 80/320+12.5/100=0.375=SI

Example 13

Synergistic activity of peracetic acid and bromonitropropanediol (BNPD)against microorganisms in paper mill service water, pH 7.0.

    ______________________________________    Biocide    (ppm product)    ______________________________________               150 min   270 min  24 Hours    ______________________________________    PAA-10       2.8 × 10.sup.6                             4.3 × 10.sup.6                                      9.0 × 10.sup.6    PAA-20       1.6 × 10.sup.5                             1.3 × 10.sup.5                                      1.5 × 10.sup.6    PAA-40       6.2 × 10.sup.3                             1.6 × 10.sup.3                                      8.5 × 10.sup.4    ______________________________________               120 min   240 min  24 Hours    ______________________________________    BNPD-25      7.2 × 10.sup.6                             5.2 × 10.sup.6                                      4.8 × 10.sup.4    BNPD-50      4.6 × 10.sup.6                             3.0 × 10.sup.6                                      2.2 × 10.sup.4    BNPD-100     3.7 × 10.sup.6                             6.4 × 10.sup.5                                      2.1 × 10.sup.3    BNPD-200     2.4 × 10.sup.6                             9.5 × 10.sup.4                                      2.7 × 10.sup.2    PAA-5/BNPD-25                 6.9 × 10.sup.6                             3.4 × 10.sup.6                                      2.5 × 10.sup.6    PAA-5/BNPD-50                 3.8 × 10.sup.6                             3.0 × 10.sup.6                                      1.1 × 10.sup.5    PAA-5/BNPD-100                 4.0 × 10.sup.6                             4.2 × 10.sup.5                                      3.4 × 10.sup.3    PAA-5/BNPD-200                 1.5 × 10.sup.6                             4.8 × 10.sup.5                                      3.8 × 10.sup.2    PAA-10/BNPD-25                 6.3 × 10.sup.5                             2.2 × 10.sup.5                                      8.7 × 10.sup.4    PAA-10/BNPD-50                 3.7 × 10.sup.5                             7.4 × 10.sup.4                                      5.6 × 10.sup.4    PAA-10/BNPD-100                 1.7 × 10.sup.5                             3.2 × 10.sup.4                                      3.8 × 10.sup.4    PAA-10/BNPD-200                 5.3 × 10.sup.4                             5.8 × 10.sup.2                                      2.3 × 10.sup.2    PAA-20/BNPD-25                 1.2 × 10.sup.5                             4.6 × 10.sup.3                                      1.4 × 10.sup.3    PAA-20/BNPD-50                 1.0 × 10.sup.5                             1.2 × 10.sup.3                                      2.6 × 10.sup.2    PAA-20/BNPD-100                 7.7 × 10.sup.4                             5.9 × 10.sup.2                                      <10.sup.1    PAA-20/BNPD-200                 5.1 × 10.sup.4                             3.5 × 10.sup.2                                      <10.sup.1    Control - 0  7.9 × 10.sup.6                             9.2 × 10.sup.6                                      6.5 × 10.sup.6    ______________________________________

Synergy Calculation:

For a 4 log₁₀ reduction after 5 hours contact:

PAA=>40 (80)

N-7639=>200 (400)

PAA/N-7639=20/100 20/80+100/400=0.5=SI

For a 5 log₁₀ reduction after 24 hours of contact:

PAA=>40 (80)

N-7639=>200 (400)

PAA/N-7639=20/100 20/80+100/400=0.5=SI

Example 14

Synergistic activity of peracetic acid and dichlorodithiol-3-one(RYH-86NA) against microorganisms in paper mill whitewater, pH=7.1.

    ______________________________________    Biocide    (ppm product)    ______________________________________               60 min   240 min  24 Hours    ______________________________________    PAA-12.5     2.3 × 10.sup.6                            8.9 × 10.sup.6                                     3.2 × 10.sup.6    PAA-25       2.7 × 10.sup.5                            3.7 × 10.sup.6                                     1.0 × 10.sup.7    PAA-50       1.2 × 10.sup.4                            2.6 × 10.sup.4                                     4.5 × 10.sup.7    ______________________________________               30 min   210 min  24 Hours    ______________________________________    RYH-86NA-5   2.6 × 10.sup.6                            3.6 × 10.sup.6                                     1.5 × 10.sup.7    RYH-86NA-10  1.4 × 10.sup.5                            2.3 × 10.sup.4                                     1.4 × 10.sup.7    RYH-86NA-20  2.3 × 10.sup.4                            4.2 × 10.sup.3                                     4.0 × 10.sup.6    RYH-86NA-40  1.4 × 10.sup.4                            4.0 × 10.sup.3                                     2.7 × 10.sup.3    PAA-10/RYH-86NA-5                 1.9 × 10.sup.5                            4.0 × 10.sup.5                                     2.9 × 10.sup.7    PAA-10/RYH-86NA-10                 4.6 × 10.sup.3                            2.8 × 10.sup.3                                     4.7 × 10.sup.6    PAA-10/RYH-86NA-20                 2.7 × 10.sup.3                            3.0 × 10.sup.3                                     2.6 × 10.sup.6    PAA-10/RYH-86NA-40                 2.5 × 10.sup.4                            3.2 × 10.sup.3                                     3.0 × 10.sup.3    PAA-20/RYH-86NA-5                 2.3 × 10.sup.4                            3.6 × 10.sup.3                                     2.7 × 10.sup.6    PAA-20/RYH-86NA-10                 4.2 × 10.sup.3                            3.4 × 10.sup.3                                     7.8 × 10.sup.6    PAA-20/RYH-86NA-20                 3.1 × 10.sup.4                            3.6 × 10.sup.3                                     3.1 × 10.sup.6    PAA-20/RYH-86NA-40                 2.5 × 10.sup.4                            1.6 × 10.sup.4                                     1.7 × 10.sup.4    PAA-40/RYH-86NA-5                 2.7 × 10.sup.4                            4.1 × 10.sup.4                                     1.9 × 10.sup.7    PAA-40/RYH-86NA-10                 1.8 × 10.sup.4                            4.6 × 10.sup.4                                     1.2 × 10.sup.7    PAA-40/RYH-86NA-20                 2.4 × 10.sup.4                            1.8 × 10.sup.4                                     1.4 × 10.sup.7    PAA-40/RYH-86NA-40                 2.6 × 10.sup.4                            2.4 × 10.sup.4                                     6.5 × 10.sup.6    Control - 0  3.5 × 10.sup.6                            1.9 × 10.sup.6                                     3.4 × 10.sup.6    ______________________________________

Synergy Calculation

For a 3 log₁₀ reduction after 4 hours contact:

PAA=>50 (100)

RYH-86NA=20

PAA/RYH-86NA=10/10 10/100+10/20=0.6=SI

PAA/RYH-86NA=20/5 20/100+5/20=0.45=SI

Example 15

Synergistic activity of peracetic acid and dichloro-n-octyl isothiazolin(RH-287) against bacteria in papermill whitewater, pH 7.1.

    ______________________________________    Biocide    (ppm product)    ______________________________________                60 min   240 min  24 Hours    ______________________________________    PAA-12.5      3.1 × 10.sup.6                             5.4 × 10.sup.6                                      3.9 × 10.sup.7    PAA-25        2.7 × 10.sup.5                             1.9 × 10.sup.6                                      5.0 × 10.sup.7    PAA-50        1.3 × 10.sup.5                             8.4 × 10.sup.4                                      7.8 × 10.sup.7    ______________________________________                30 min   210 min  24 Hours    ______________________________________    RH-287-25     4.6 × 10.sup.6                             1.5 × 10.sup.7                                      6.4 × 10.sup.7    RH-287-50     4.1 × 10.sup.6                             1.2 × 10.sup.7                                      3.6 × 10.sup.7    RH-287-100    4.6 × 10.sup.6                             2.3 × 10.sup.6                                      2.8 × 10.sup.7    RH-287-200    3.9 × 10.sup.6                             1.1 × 10.sup.5                                      2.6 × 10.sup.7    PAA-10/RH-287-25                  3.8 × 10.sup.6                             5.4 × 10.sup.6                                      5.8 × 10.sup.7    PAA-10/RH-287-50                  3.4 × 10.sup.6                             2.0 × 10.sup.6                                      3.8 × 10.sup.7    PAA-10/RH-287-100                  2.1 × 10.sup.6                             1.3 × 10.sup.5                                      2.4 × 10.sup.7    PAA-10/RH-287-200                  7.3 × 10.sup.5                             2.0 × 10.sup.4                                      2.3 × 10.sup.7    PAA-20/RH-287-25                  5.1 × 10.sup.5                             4.8 × 10.sup.5                                      6.3 × 10.sup.7    PAA-20/RH-287-50                  4.4 × 10.sup.5                             1.8 × 10.sup.5                                      6.1 × 10.sup.7    PAA-20/RH-287-100                  3.2 × 10.sup.5                             5.0 × 10.sup.4                                      3.5 × 10.sup.7    PAA-20/RH-287-200                  1.2 × 10.sup.5                             7.3 × 10.sup.3                                      2.3 × 10.sup.7    PAA-40/RH-287-25                  2.3 × 10.sup.5                             7.1 × 10.sup.4                                      6.1 × 10.sup.7    PAA-40/RH-287-50                  2.1 × 10.sup.5                             4.0 × 10.sup.4                                      6.2 × 10.sup.7    PAA-40/RH-287-100                  1.5 × 10.sup.5                             2.3 × 10.sup.4                                      4.7 × 10.sup.7    PAA-40/RH-287-200                  2.0 × 10.sup.5                             1.9 × 10.sup.4                                      2.0 × 10.sup.7    Control - 0   4.8 × 10.sup.6                             4.6 × 10.sup.6                                      2.3 × 10.sup.7    ______________________________________

Synergy Calculation:

For a 3 log₁₀ reduction after 4 hours contact:

PAA=>50 (100)

RH-287=>200 (400)

PAA/RH-287=20/200 20/100+200/400=0.7=SI

Example 16

Synergistic activity of peracetic acid and1-(3-chloroallyl)-3,5,7-triaza-1-azoniaadamantane chloride (D75) againstbacteria in papermill whitewater, pH 7.1.

    ______________________________________    Biocide    (ppm product)    ______________________________________                  60 min 240 min    ______________________________________    PAA-25          1.6 × 10.sup.5                             1.7 × 10.sup.5    PAA-50          1.4 × 10.sup.4                             2.0 × 10.sup.5    PAA-100         3.2 × 10.sup.3                             2.0 × 10.sup.2    ______________________________________                  30 min 210 min    ______________________________________    D75-50          4.0 × 10.sup.5                             7.2 × 10.sup.4    D75-100         3.7 × 10.sup.5                             6.7 × 10.sup.4    D75-200         2.9 × 10.sup.5                             6.0 × 10.sup.4    D75-400         3.5 × 10.sup.5                             6.3 × 10.sup.4    PAA-10/D75-50   2.4 × 10.sup.5                             9.9 × 10.sup.4    PAA-10/D75-100  2.1 × 10.sup.5                             5.8 × 10.sup.4    PAA-10/D75-200  1.6 × 10.sup.5                             2.5 × 10.sup.4    PAA-10/D75-400  1.9 × 0.sup.5                             2.8 × 10.sup.3    PAA-20/D75-50   2.1 × 10.sup.5                             1.1 × 10.sup.5    PAA-20/D75-100  2.6 × 10.sup.5                             8.7 × 10.sup.4    PAA-20/D75-200  2.6 × 10.sup.5                             1.6 × 10.sup.5    PAA-20/D75-400  2.2 × 10.sup.5                             8.2 × 10.sup.3    PAA-40/D75-50   1.9 × 10.sup.5                             8.1 × 10.sup.4    PAA-40/D75-100  2.0 × 10.sup.5                             1.1 × 10.sup.5    PAA-40/D75-200  1.8 × 10.sup.5                             5.2 × 10.sup.4    PAA-40/D75-400  1.6 × 10.sup.5                             6.5 × 10.sup.3    Control - 0     6.1 × 10.sup.5                             2.5 × 10.sup.6    ______________________________________

Synergy Calculation:

After 4 hours of contact, a 2 log₁₀ reduction was achieved with:

PAA=100

D75=>400 (800)

PAA=10 ppm/D75=400 ppm

SI=10/100+400/800=0.60

Example 17

Synergistic activity of peracetic acid and bis(trichloromethyl) sulfone(BTCMS) against bacteria in paper mill whitewater, pH 7.1.

    ______________________________________    Biocide    (ppm product)    ______________________________________               60 min    240 min  24 Hours    ______________________________________    PAA-25       7.0 × 10.sup.5                             8.0 × 10.sup.5                                      1.7 × 10.sup.6    PAA-50       7.0 × 10.sup.5                             1.9 × 10.sup.6                                      5.4 × 10.sup.6    PAA-100      8.0 × 10.sup.5                             8.1 × 10.sup.5                                      9.6 × 10.sup.6    ______________________________________               30 min    210 min  24 Hours    ______________________________________    BTCMS-10     5.0 × 10.sup.5                             8.0 × 10.sup.4                                      8.4 × 10.sup.6    BTCMS-20     1.1 × 10.sup.6                             1.2 × 10.sup.5                                      9.2 × 10.sup.6    BTCMS-40     8.0 × 10.sup.5                             5.9 × 10.sup.4                                      1.7 × 10.sup.6    BTCMS-80     1.1 × 10.sup.5                             4.6 × 10.sup.4                                      1.3 × 10.sup.5    PAA-10/BTCMS-10                 1.5 × 10.sup.6                             6.0 × 10.sup.5                                      8.6 × 10.sup.6    PAA-10/BTCMS-20                 4.0 × 10.sup.5                             6.5 × 10.sup.4                                      4.6 × 10.sup.6    PAA-10/BTCMS-40                 1.1 × 10.sup.5                             6.3 × 10.sup.3                                      5.1 × 10.sup.4    PAA-10/BTCMS-80                 5.1 × 10.sup.4                             4.7 × 10.sup.2                                      4.5 × 10.sup.2    PAA-20/BTCMS-10                 1.1 × 10.sup.5                             1.0 × 10.sup.5                                      6.0 × 10.sup.6    PAA-20/BTCMS-20                 3.0 × 10.sup.5                             1.1 × 10.sup.3                                      1.1 × 10.sup.7    PAA-20/BTCMS-40                 1.0 × 10.sup.5                             8.5 × 10.sup.2                                      2.0 × 10.sup.6    PAA-20/BTCMS-80                 2.6 × 10.sup.4                             6.0 × 10.sup.3                                      1.2 × 10.sup.3    Control - 0  9.0 × 10.sup.5                             1.4 × 10.sup.6                                      2.0 × 10.sup.6    ______________________________________

Synergy Calculation:

For a 3 log₁₀ reduction after 4 hours contact:

PAA=>100 (200)

BTCMS=>80 (160)

PAA=10 ppm/BTCMS=40 ppm

SI=10/200+40/160=0.30

PAA=20 ppm/BTCMS=20 PPM

SI=20/200+20/160=0.225

For a 3 log₁₀ reduction after 4 hours contact:

PAA=>100 (200)

BTCMS=>80 (160)

PAA=10 ppm/BTCMS=80 ppm

SI=10/200+80/160=0.55

PAA=20 ppm/BTCMS=80 PPM

SI=20/200+80/160=0.60

Example 18

Synergy Study: Combination of Peracetic acid (PAA) and Isothiazolinone

Organism Used: Pseudomonas aeruginosa (PA01), typical cooling waterbacterium

Water used: Synthetic cooling water (standard no. 13, adjusted to pH of7.0)

    ______________________________________                    Time = 0 Time = 17 hours                    CFU/ML   CFU/ML    ______________________________________    Control (No added biocide)                      9.3 e6     2.0 e7    Peracetic Acid (PAA) - only     4 ppm as product            2.7 e7     8 ppm as product            1.5 e6    16 ppm as product            4.7 e4    32 ppm as product            4.7 e3    40 ppm as product            2.0 e2    Isothiazolinone - only     10 ppm as product           5.7 e6     20 ppm as product           1.0 e6     40 ppm as product           1.0 e6     50 ppm as product           6.4 e5     75 ppm as product           7.7 e4    100 ppm as product           4.0 e3    Peracetic acid (5 ppm as product) +    Isothiazolinone     10 ppm as product           2.3 e5     20 ppm as product           1.0 e5     40 ppm as product           3.0.e3     50 ppm as product           2.7 e3     75 ppm as product           1.2 e3    100 ppm as product           4.0 e2    Peracetic acid (10 ppm as product) +    Isothiazolinone     10 ppm as product           5.4 e4     20 ppm as product           4.4 e3     40 ppm as product           5.7 e3     50 ppm as product           7.2 e2     75 ppm as product           1.0 e2    100 ppm as product           4.8 e2    ______________________________________     Synergy Index:(5 ppm PAA + 40 ppm Isothazolinone: 0.125 + 0.5 = 0.525     (<1.0), Synergistic

Example 19

Synergistic activity of peracetic acid and1-(3-chloroallyl)-3,5,7-triaza-1-azoniaadamantane chloride (D75) againstbacteria in a 55% solids Kaolin clay slurry, pH 8.3.

    ______________________________________    Biocide    (ppm product)                 1 Day       1 Week   4 Weeks    ______________________________________    PAA-500      6.0 × 10.sup.5                             3.1 × 10.sup.7                                      >10.sup.7    PAA-1000     <10.sup.3   5.0 × 10.sup.7                                      >10.sup.7    PAA-2000     5.8 × 10.sup.6                             9.8 × 10.sup.7                                      >10.sup.7    D75-250      <10.sup.3   <10.sup.3                                      >10.sup.7    D75-500      <10.sup.3   <10.sup.3                                      2 × 10.sup.3    D75-1000     <10.sup.3   <10.sup.3                                      3 × 10.sup.3    PAA-500/D75-500                 <10.sup.3   <10.sup.3                                      <10.sup.3    Control - 0  9.7 × 10.sup.4                             >10.sup.7                                      >10.sup.7    ______________________________________

Synergy Calculation:

To achieve an endpoint of <10³ CFU/mL for 4 weeks of contact:

PAA=>2000 ppm (4000)

D75=>1000 ppm (2000)

PAA=500/D75 =500

SI=500/4000+500/2000=0.375

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present invention andwithout diminishing its attendant advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims:

We claim:
 1. A composition for inhibiting the growth of microorganismsin aqueous systems comprising effective amounts of peracetic acid and anon-oxidizing biocide selected from the group consisting of:decylthioethylamine, orthophthaldehyde, dodecylguanidine hydrochloride,1-(3-chloroallyl)-3,5,7-triaza-1-azoniaadamantane chloride, dibromodicyanobutane and bis(trichloromethyl)sulfone, said amount of peraceticacid and non-oxidizing biocide being selected to result in a synergyindex of less than 1 wherein said synergy index is calculated bydetermining a first ratio of the amount of peracetic acid required toproduce a level of microorganism growth inhibition when added incombination with the amount of non-oxidizing biocide to the amount ofperacetic acid required to produce the level of growth inhibition in theabsence of the non-oxidizing biocide, and adding the first ratio to asecond ratio of the amount of non-oxidizing biocide required to producethe level of growth inhibition when added in combination with the amountof peracetic acid to the amount of non-oxidizing biocide required toproduce the level of growth inhibition in the absence of the peraceticacid.
 2. The composition of claim 1 wherein the amount of peracetic acidranges from approximately 5 to 250 ppm and the amount of non-oxidizingbiocide ranges from approximately 10 to 250 ppm.
 3. A method forcontrolling the growth of microorganisms in industrial process waterincluding the step of administering a sufficient amount of a peraceticacid and a sufficient amount of a non-oxidizing biocide to theindustrial process water to inhibit the growth of the microorganisms,said non-oxidizing biocide selected from the group consisting ofdecylthioethylamine, orthophthaldehyde, dodecylguanidine hydrochloride,1-(3-chloroallyl)-3,5,7-triaza-1-azoniaadamantane chloride, dibromodicyanobutane and bis(trichloromethyl)sulfone, said non-oxidizingbiocide being selected to result in a synergy index of less than 1wherein said synergy index is calculated by determining a first ratio ofthe amount of peracetic acid required to produce a level ofmicroorganism growth inhibition when added in combination with theamount of non-oxidizing biocide to the amount of peracetic acid requiredto produce the level of growth inhibition in the absence of thenon-oxidizing biocide, and adding the first ratio to a second ratio ofthe amount of non-oxidizing biocide required to produce the level ofgrowth inhibition when added in combination with the amount of peraceticacid to the amount of non-oxidizing biocide required to produce thelevel of growth inhibition in the absence of the peracetic acid.
 4. Themethod of claim 3 wherein the industrial process water is selected fromthe group consisting of water of a pulp and paper mill system, coolingwater and mining.
 5. The method of claim 3 wherein the peracetic acidand the non-oxidizing biocide are added in a ratio from about 10:1 to1:25.
 6. The method of claim 3 wherein the amount of peracetic acidadded ranges from approximately 5 to 250 ppm and the non-oxidizingbiocide ranges from approximately 10 to 250 ppm.
 7. The method of claim3 wherein the microorganisms contain bacteria.
 8. The method of claim 3wherein the microorganisms contain fungi.
 9. The method of claim 3wherein the peracetic acid is added to the industrial water prior to theaddition of the non-oxidizing biocide.